The embodiments described herein relate generally to the field of ophthalmic therapies and more particularly to the use of a microneedle for delivery and/or removal of a substance, such as a fluid therapeutic agent into and/or from ocular tissues for treatment of the eye.
Although needles are used in transdermal and intraocular drug delivery, there remains a need for improved microneedle devices and methods, particularly for delivery of substances (e.g., drugs) into the posterior region of the eye. Many inflammatory and proliferative diseases in the posterior region (or other regions) of the eye require long-term pharmacological treatment. Examples of such diseases include macular degeneration, diabetic retinopathy, and uveitis. It is often difficult to deliver effective doses of a drug to the back of the eye using conventional delivery methods such as topical application or an intravitreal administration (IVT), which has poor efficacy, and systemic administration, which often causes significant side effects. For example, while eye drops are useful in treating conditions affecting the exterior surface of the eye or tissues at the front of the eye, the eye drops are often not sufficiently conveyed to the back of the eye, as may be required for the treatment of some of the retinal diseases listed above.
Although there have been advances in the past decade regarding the utilization of systemically delivered substances, there are obstacles to wide spread adoption of such methods. For example, in certain situations, direct injection into the eye (e.g., into the vitreous) using conventional 27 gauge or 30 gauge needles and syringes can be effective. Direct injection, however, can be associated with significant safety risks, and physicians often require professional training to effectively perform such methods. Moreover, in some instances, targeted injection of a therapeutic agent is desirable. In such instances, however, the relatively small anatomic structures of the eye often result in significant challenges to placing a needle at a target location using known devices and methods, especially as they pertain to placing the distal end of the needle at the desired depth within the eye. Furthermore, IVT administration can have side effects such as increased intraocular pressure or faster onset of cataract formation.
In addition, many known methods of direct injection of a drug into the eye include inserting a needle or a cannula at an acute angle relative to a surface of the eye, which can make controlling the depth of insertion challenging. For example, some such methods include controlling the angular orientation of the needle such that the injected substance exits the needle at a particular location. Moreover, some known methods of injecting substances into ocular tissue include using complicated visualization system or sensors to control the placement of the needle or cannula.
Known devices for ocular injection do not provide the mechanism for adjusting needle length so that the needle can be inserted into the eye to the desired depth. Known systems also do not provide a reliable mechanism for determining when the needle tip is in the desired location, for example, the suprachoroidal space (SCS) of the eye. Such shortcomings in known systems and methods are exacerbated because the size and thickness of various layers included in the eye can vary substantially from one person to another. For example, the thickness of the conjunctiva and the sclera can be substantially different and their true value cannot easily be predetermined via standard techniques. Furthermore, the thickness of these layers can also be different in different portions of the eye and at different times of the day in the same eye and location. Therefore, using known systems and methods it can be challenging to determine and/or adjust the length of the needle for puncturing the eye, such that a tip of the needle is at the desired depth, for example, the SCS. Too short a needle might not penetrate the sclera, and too long a needle can traverse beyond the SCS and damage the retina of the eye. Further, known systems do not provide a convenient way to detect the position of the needle tip within the eye.
Because of the sensitivities associated with intraocular injection (e.g., the sensitivity of the tissue, the potential impact on intraocular pressure and the like), many known systems involve manual injection, often using needles and/or cannulas having a small diameter (e.g., 27 gauge, 30 gauge, or even smaller) and lengths of 12 mm, 15 mm or even longer. More particularly, many known devices and methods include the user manually applying a force (e.g., via pushing a plunger with their thumb or fingers) to expel a fluid (e.g., a drug) into the eye. Because of the small needle size and/or the characteristics of the injected drug, some such devices and methods involve the use of force levels higher than that which users are comfortable with applying. For example, some studies have shown that users generally do not like to apply more than 2N force against the eye during ocular injection. Accordingly, in certain situations a user may not properly deliver the medicament using known systems and methods because of their reluctance to apply the force to fully expel the medicament.
Moreover, injection into different target layers of the eye can cause variability in the amount of the force required for insertion of the needle and/or injection of the medicament. Different layers of the eye can have different densities. For example, the sclera generally has a higher density than the conjunctiva or the SCS. Differences in the density of the target region or layer can produce different backpressure against the needle exit, i.e., the tip of the needle from which the fluid emerges. Thus, injection into a relatively dense ocular material such as sclera requires more motive pressure to expel the medicament from the needle than is required when injecting a medicament into the SCS.
Furthermore, the injection force to expel the medicament also depends on the density and viscosity of the liquid medicament, length of the needle, and/or diameter of the needle. To inject certain medicaments into the eye via desired needles (e.g., 27 gauge, 30 gauge, or even smaller) can require more force than many practitioners are comfortable (or capable of) applying.
Thus, a need exists for improved devices and methods, which can assist in facilitating injection of a viscous medicament into ocular tissue.